The present invention relates to a fuel injector.
German Patent Application No. 196 26 576 describes an electromagnetically actuatable fuel injector for directly injecting fuel into the combustion chamber of an internal combustion engine. In the fuel injector, for the purpose of electromagnetic actuation, an armature cooperates with an electrically excitable solenoid coil, and the lift of the armature is transmitted via a valve needle to a valve-closure member. The valve-closure member cooperates with a valve seat surface to form a sealing seat. Resetting the valve needle and the valve-closure member is accomplished using a resetting spring.
Especially disadvantageous in the fuel injector described in German Patent Application No. 196 26 576 are relatively long closing times. Delays in closing the fuel injector are caused by the adhesion forces operating between the armature and the internal pole and by the non-instantaneous subsiding of the magnetic field when the excitation current is switched off. Therefore, the resetting spring must have a large spring constant, i.e., a large biasing. To achieve shorter closing times, the resetting force must be dimensioned significantly greater than would be necessary for sealing off the combustion chamber pressures. This necessitates high power requirements for the electronic drive circuit.
The fuel injector according to the example embodiment of the present invention has the advantage that an additional cutoff spring acts positively both on the opening as well as on the closing process. The opening process is accelerated by the lesser spring force of the resetting spring, which makes possible lower drive power levels. In the closing process, an additional acceleration force is made available by the additional , so as to close the fuel injector rapidly. The spring constant of the resetting spring is dimensioned such that the spring force exerted is still quite sufficient to seal the fuel injector against the pressure in the combustion chamber of the internal combustion engine. In response to the cutoff, the rapid acceleration of the valve needle is taken over by the , which is dimensioned at a larger spring constant than the resetting spring. In the opening motion, the is biased in only a relatively short partial lift. Since, when this partial lift is completed, the maximum magnetic force is already built up, the opening motion is only delayed by the to an insignificant extent.
The variable configuration of the is advantageous, which is not limited to spiral springs, but can also be executed as planar or sleeve-shaped disk springs. Using a disk spring has the advantage of a sloping force curve.
Also advantageous is the simple manufacture and assembly of the components, which make no special demands on the material or on the manufacturing process.